Extractive distillation process



Sept. 9, 1952 W. M. DROUT, JR

EXTRACTIVE DISTILLATION PROCESS Filed April 1, 1949 [SOLVENT Edi [Liam m..Droui,.Jn {Inventor 5 Q gk. clbbor'rzes Patented Sept. 9, 1952 510,141 :nxraao rrvs ms'r LLAnoN. rnocsss :Drout,..Jr., Linden} N. J.,asslgnor to Standard 011 Development Company, a corpo- "ration of Delaware 1 "Appllcation'April 1, 1949, Serial No. 84,987

This application is a "continuation-impart of U. S. Patent application SerialNo."24,626,filed MayiflMB.

c Claims. (01. 202-3915).

"I his invention relates-to the :puriflcatlon of orpanic liquids and -vapors'. ."More I specifically the invention relates .an improved extractive distillation process ior the purification of organic liquids and vapors. In particular the invention .processin which the external is-obtained by..extracting the non-solvent phaseof ,the distil late with the extractive distillation solvent.

. It is another object of this invention to provide a novel and improved process for thepnrifica'tion of alcohols, particularly alcohols of .2 to .5 carbon is concerned with the purification of organicliquids "bywextractine distillation in which 9 the distillation is carriedvrout inithepresence of a selective external refluxwobtained the extract phase by extracting the nonrsolvent"phase of the overhead'withthe solyent employed .inthe extractive distiliationpperation.

The invention has wide application and may be employed in extractive distillation operations wherein the distillate is non-homogeneous to accomplish, among others, the following separa- 1 tions: an alcchol from impurities boiling over a Wide range and which are insoluble in the distillation solvent; oneor *more' alco'hols "from'other close-boiling alcohols; alcohols from other oxygenated compoundsfsuch as ketones, aldehydes, esters, etc; water iromlore'anic compounds such asalcohols, ketches, eta; hydrocarbons from their isomers such as .mezta xylenerfrom para xylene; paraflins fromolefins, olefinsfrom .diolefins; etc.

In'each of the .above mentioned applications the appropriate solvent suitable for the separation, e. g., water, aqueous salt solutions, acetone. hydrocarbon oils, aroma-tic ethers, etc .is. employed duringthe extractive distillation process. Howeverrtheprocess .of thisinvention is applicable to extractiveldistillations of .all types, i."e., regardless of the separation being made .or the particular. solvent emplcyedgprovidedathe component being removed overhead insolublein the .distillation solvent. The invention is particularly applicable tothose distillations where the overheadseparates into two .phases .or where phase separation canbe readily induced, e. g, by chang ing the temperature of. the distillate or by the addition of anothercomponent "to the distillate. The non-solvent phase of the distillateisextracted with theisolven-t and theresultinglextract isrefluxed torthe extractive distillationxcolumn. j

. Jtds an :obiectcf this inventionzthereforeto atoms produced by the reaction of mono-olefins, by removing therefrom impurities both water- :soluble .and water insoluble and odor-producing contaminants; I

Theserand other objects of .the invention are accomplished :by subjecting the organic liquid to extractive .distillationin a distillation :zone in the presenceof anextractive distillation solvent the nature, condition and amounts of which are determined by the purification being effected, and carrying out the distillation in the presence of an .external reflux .consistingcof the solvent phase obtained by extracting the nonsolvent phase of thedistilla-tewith the extractive distillation solvent. r

-Although the invention is applicable "to the separations listed above :among othersiit is particularly applicable to the purification'of' aliphatic alcohols especially those of 2 to -5 carbon atoms per molecule prepared from mono-olefins either by acid, -.catalysed-.hy.dration or byzthe so-called oxo-synthesis oi anwolefin with carbon monoxide followed by hydrogenation.

r .This invention will be describedimitsapplicartionto the purification .of :crude alcohols produced from mono olefins but it is to be understood'that theinvention is notlimited thereto since it hasuequalapplication to other extractive distillations regardless of the separations being effected providedthedistillate Jupon condensation is di-phase.

By operating .according'to the terms of this invention high yields of highly refined alcoholof excellent odor characteristics can be produced for use in specialized industries, such as the cosmetic, perfume, drug, biological and vitamin industries. Henetofore, isuchalcohols were obtained only in very poor yields and'at high cost by repeated reprovide a process for the purification of organic fractionations of partially refined alcohols.

LIn or'der to show thenumber and diversity of the impurities present "in alcohol resulting "from catalyzedhydration processes; the "following :analysis is-rgivenfor a sample of crude isopropanol produced by the sulfuric acid hydration of propylene, the proportions are based on an anhydrous alcohol basis:

Isopropanol 90 volume percent Diisopropyl ether -10 volume percent Acetone Hydrocarbons (B. P. 60-300" 0., major portion 100-300 C.)

Oxygenated compounds other than acetone incl. ethers, tertiary butyl alcohol and higher alcohols, higher ketones, etc.

Traces of sulfur 1 compounds, boiling over a wide range up to 2 vol. percent Atypical analysis of a sample of the polymer' j product, in this case the so-called propyl oil.

resulting from the production of isopropanol by the sulfuric acid hydration of propylene, is as follows: i I

55 weight percent secondary-heptanol (B. P.

21 weight percent 'secondary-octanol (B. P.

According to this invention the crude aqueous alcohol mixture containing the impurities above described is subjected to a distillation operation in which the crude homogeneous alcohol solution is fed to a distillation tower at a point below the top, preferably at about the mid-point of the tower, and in which water is fed to the top of the tower or at a point near the top thereof in sufilcient' quantity to maintain a composition of 65-999 mol percent in the liquid phase in the column; Ihe operable water concentration as determined by the water solubility of the alcohol will vary with the crude alcohol mixture being purified, e. g ethanol 65-99 mol percent, preferably 80-99 mol percent; isopropanol 70-99 mol percent, preferably 85-99 mol percent; secbutanol 95-99.!) mol percent; and sec-amyl alcohols 97.5-99.9 percent. Operation at elevated temperature and pressure greatly broadens the solubility range of secondary butanol and secondary amyl alcohol. For example, at 107 C. secondary butanol is completely miscible with water, and at 188 C. Secondary amyl alcohol is completely miscible with water. Another method of' enhancing the solubility of secondary butanol and sec-pentanol is the addition of low molecular weight'oxygenated compounds, such as low molecular weight therefrom by decantation.

4 solvent, i. e., water and the extract phase is refluxed to the column.

Many of the impurities taken overhead boil normally at a temperature above the boiling point of the alcohol which is being purified, e. g., the polymer oils which boil as high as 250 C. to 300 C. Additional polymer oil impurity, particularly a portion of the higher boiling fractions thereof, concentrates in the column at a point near the alcohol feed plate upon contact of the crude alcohol feed with the internal aqueous reflux. This concentration of polymer oil occurs near the alcohol feed plate; A stream containing the polymer concentrate is removed from theldistillation column at this point and the polymer" removed The dilute alcohol phase is returned to the column at a point about one plate below the withdrawal point. In this manner practically all the odor-producing con- ,taminants are removed from the alcohol. The

dilute aqueous alcohol product obtained as botalcohols. In the case of sec-pentanol, acetone may be employed as a solubilizer.

The water thus supplied is suflicient to permit taking overhead all or substantially all of the impurities, particularly the water-insoluble impurities, contained in the crude alcohol, namely, the ethers, ketones, other alcohols, light hydrocarbons some of which impurities boil as low as 30 0., and even all or a substantial portion of the high boiling polymer oils. The distillation tower is operated without the conventional external reflux of part or all of the total distillate condensate. Instead the column distillate is condensed and the non-solvent phase of the distillate is extracted with the extractive distillation toms from the distillation zone and containing between -99 mol percent water is led to a concentrating column, wherein the desired alcohol is concentrated and recovered in high yields. The product is far superior in odor to any alcohol obtained by any of the purification -methods known to the art.

If desired, the crude aqueous alcohol may be treatedpriorito the extractive distillation step, with additional amounts of water tothrow out of solution the bulk of the polymer oil, particu-- larly the higher boiling constituents of the polymer oil. l

It has been found=that vol. percent of the alcohol present in a crude aqueousisoprop'yl 'alcohol from'the hydration of propylene having the following composition; can be recovered as high purity, excellent odoralcohol, by concentrating the weak alcohol recovered as-bottoms vfrom a 45 plate water extractive distillation column:

65 vol. percent isopropanol V 1.4 ,vol. percent propyl oil (based content).

0.2 vol. percent acetone (based on alcohol content) 5.1 vol. percent isopropanol ether (based on alcohol content) Balance-water and other impurities In application Serial No. 68,453 flied December 31, 1948 and assigned to the present assignee, there is described an extractive distillation process in which the customaryexternal reflux is omitted so that vapors are removed from the distillation column without further condensation above the point of entry of the extractive distillation solvent. As described in said application with reference to alcohol purification optimum quality alcohol can be obtained by operating the extractive distillation column with no external reflux. However, if the number of plates in the extractive distillation column is small enough so that excessive alcohol loss from the top of the column occurs then the selective reflux principle of this invention is recommended. This selective reflux is obtained in the case of alcohol purification by water extratcing the non-aqueous phase of the condensed distillate and refluxing the re sulting extract in whole or in part to the extractive distillation zone.

'The accompanying drawing represents a flow plan .in elevation of. one process and accomtpanying apparatus for carrying out this invenion. r

on alcohol iReferring to the drawing, numeral! r presents an extractivedistillation tower, such as a 45 plate column, to which crude isopropyl alcohol or partially refined isopropyl alcohol containing 0 to 60- vol. per cent water is via line i. The feed line i is locatedat: a point preferablyk above the midsection .of the distillation column, for example,-at about thefBOth plate in a :45 plate tower. Water is fed to the tower in considerable amounts through line 3. The water is fed to the top or near the top of the tower but always above the alcohol feed plate. To obtain the desired separation of the impurities from the alcohol, themixtureis' subjected-to a continuous fractional distillation in column 2; The'water introduced in sufficiently large quantity at the upperp'art of thetower effectively modifies the relative volatilities of the organic compounds being separated, and distillation :of. an extremely large part ef 'the impurities from the alcohol 'is'effected. The temperature. of the water feed to the extractivedistillation :zone is :preferalblyclose to thetemperature of the liquid on the water feed plate, althrough it imay he "lower to partially condense vapors ascending "to the water feed plate. For contimious eflicient operation, the water must be added continuously "near the top of the column while, the "crude. alcohol being purified is continuously fed into the column. atta lower point and while rsulficient .:heat is 'provided to afford distillation throughout the column. The .:feed stream may he preheated to a temperature close to that of the internal liquid reflux under equilibrium boiling conditions at .thezpoint of introduction. The preheated alcohol feed stream may be liquid, partially vaporized or completely vaporized when introduced into the fractionation column. Vapors of the organic compounds introduced as a feed stream pass upwardly through the distillation zone in contact with descending internal liquid reflux under equilibrium reboiling and refluxing conditions. Due to the fact that water, considerably in excess of the amount of water distilled, iszintroduced to mix with the condensate near theitop ofithe distillation .zone, the water concentration inthe internal liquid reflux at the top of Jthe"distillation zone is higher than the water concentration in vapors passing up through the. zone. Contrasted therewith in normal rectification of al cohols from an aqueous yfeed, thewater concention diminishes rapidly toward the limiting water concentration -of-the aqueous azeotropes in the vapors ascending the distillation; column.

The quantity of water required to beintroduced continuously at the upper part of the distillation zone for accomplishing :the "desired separation of the impurities from the alcohol is considerably greater than thequantity or" condensate with which it'r-becomes homogeneously mixed on each plate in order to makethewater concentration of the internal reflux substantial- 1y above a critical minimum :in the range of 70-99.!) mol per cent. With adequate water concentration in the internal reflux for effecting the separation, the alcohol to be isolatedfiin the aqueous bottoms is dissolved in the aqueous internal reflux that reaches the bottom of the distillation column. Excellent" quality isopropyl alcohol was obtainedby adjusting the alcohol to water feed'ratio so that'15-25 vol. per cent alcohol was obtained from the bottom of the distillation column.

Referring to'the drawing, impurities contained in the isopropyl alcohol, namely, isopropyl ether,

acetone; a substantial part of the propyl oil; etc; 7

and a small percentage orthe solvent' water which is carrie'doverhead are removed as distillatevialine 4 condensed and leadto decanter 5. Inthe decanterthe condensate separates into two phases, namely, an aqueous-phase 1 and an organic phase 6. The organic phase is'lead via line t to an extraction zone!) entering at a pointatthe midsectionthereof. In the extraction zone the organic phase is countercurrently extracted with water entering at a point-near the top of the extraction zone via line I0. In the extraction zone the materials separate into a raflinate phase consisting of hydrocarbons .andother water insoluble materials. This-phase is withdrawn via line H. The aqueousextract phase is withdrawn via line 12 and refluxed to the top of the distillation zone 2 vialine 12 together with the aqueous phase which is removed irom decanter 5 vialine It. It is alsowpossibleito return the reflux in whole 0 inlpartxthroughsolvent'ffeed lineIB. .Itis alsorwithin .the :scope of "this invention to :add .the entire :ramount. of distillation solvent toxthe system :via line will. In this event the solvent feediline 3;.may benispensed'with. l

a .The overhead condensate-has beenirepresented as separating'into annpperuorganic phase and a lower aqueous phase. It :should 'bep bo'rne in mind that in 'somedistillations, for example; in which ahydrocarbonsolvent is employed as an extractive distillation solvent the upper phase would be the solvent phase while the lower phase would be the non-solvent phase. :Likewise'the same situation would occur 'in-the* extraction zone wherein the upper phase depending, upon the solvent employed may become the extract phase-and the lower phase the rafiinate phase. In any event it is the non-solvent phase of the condensated distillate which is extracted in the extraction zone whichiis returned tothe distillation zone as reflux. l

Although the overhead from the distillation column contains approximately "5 volume per cent of the isopropyl. alcoholsfed to thexdistilla tion zone it is possible by employingoptimum distillation .ICOIlditl'Ql'lS to hold the alcohol content of theoverhead to a much smaller amount, say about 1 volume-per cent. :I-Iowever, if an extremely pure product is desired, e. 'g., practically pure alcohol, it may be attained'at the expense. of additional alcoholgoing overhead withthe impurities being. removed. This alcohol is recovered by extraction of the overhead organic phaseand isreturned tothe distillation zone togetherwith the aqueous phase of the condensed distillate.

Additional high boiling polymer .oil has been found .to concentrateas a separate phase in column 2 at a point near the alcohol feed plate when the feed ismixed with the aqueous reflux stream. A sidestream containing this polymer oil concentrate is removed from the column and the polymer .oil is separated by continuous decantation, thus minimizing or virtually eliminating polymer oil from the concentrating column. This 'sidestream lSI'Bl'IlOVBd from the column at a point below the crude alcohol feed plate, but preferably at a point immediately below the alcoholieedplate. "To this end a'stream can be removed from "tower 2 via 'line 26 and sent to decanter 21. This stream is withdrawn at a point near the alcohol feedplate or slightly belowthe alcohol feed plate; In the decanter the stream separates into an upper polymer oil phase 28 which is discarded, and a lower aqueous alcohol phase 29 freed of polymeroil; The latter is returned to the tower via-line 30 at a pointabout a plate below the withdrawal point.

Bottoms'from the tower 2, consisting chiefly of aqueous alcohol of about 10-40 vol. per cent, preferably 15-25 vol. per cent is removed via line H and introduced to concentrating column l5. Part of the aqueous bottoms is withdrawn from line l4 via line 32 and sent to reboiler SI for heating by indirect or direct heat exchange with a heating medium such as live steam, and returned via line 33 to the distillation column. In column IS the aqueous alcohol is concentrated to the desired level up to the 91.3 vol. per cent isopropyl alcohol-water azeotrope, which is removed as a sidestream near the top of the column via line [6. The remaining propyl oil,'if any, contained in the aqueous alcohol is removed from the concentrating column in a 'sidestream I! at a point about three'plates above the feed plate. Some remaining traces of light material, if any, and alcohol are removed overhead via line 18, condensed in condenser 19 and removed from the system. If desired, this overhead may be recycled to the feed to the extractive distillation zone. Part of the condensate may be refluxed to the top of the column via line 20. toms from the concentrating column consisting substantially of water are removed via. line 21 and may be recycled by line 22 inwhole or in part to the extractive distillation tower 2 via water supply line 3. Excess Water may be removed from the system via line 2|. of the aqueous bottoms may be withdrawn via line 23 and sent to reboiler 24 for heating by indirect or direct heat exchange with a heating medium such as live steam and recycled to column [5 via line 25. Although the dilute aqueous alcohol solution from the distillation zone has been described as concentrated by fractional distillation, other means of concentration may be employed, such as solvent extraction.

In the separation of impurities from isopropanol produced by the acid catalyzed hydration of propylene, essentially no satisfactory separation is effected if the internal reflux contains less than '70 mol per cent water. For obtaining satisfactory results on a practical scale the preferred range is 85-99 mol per cent water in the internal reflux. I

Under steady conditions in the extractive distillation zone, the internal reflux, having adequate water concentration for accomplishing the separation of the wide-boiling impurities, tends to have a nearly constant water concentration in a preferably homogeneous liquid phase at each plate, and the high water concentration is approximately uniform in the internal reflux below the alcohol feed plate. This internal reflux in flowing from the top to the bottom of tower becomes richer in the alcohol while the other impurities of the feed become distilled overhead. In the distillation process the mol per cent water in the total overhead from the extractive distillation column will vary with the operating conditions and with the nature of the. impurities rejected overhead. The aqueous bottoms removed from the extractive distillation zone will contain approximately 70-99 mol per cent water. The overhead from the extractive distillation zone upon condensation and cooling separates into two phases, .an aqueous phase and an organic phase. An Engler distillation of a typical organic phase, resulting from the purification of isopropanol reveals that the initial boiling point lies between not- A portion 40-50" C., and the final boiling point, is approximately 250 C., indicating that'there-is considerable high boillng material contained in the overhead. a

' Without attempting to explain the mechanism by which the desired separation occurs in the distillation column, it can be said that the process isone of vapor-liquid extraction in which the vapors contain a greater-relative concentration of the impurities than under the normal fractionation conditions in the absence of the considerable amount of water internal reflux. It is evident from the results obtained that the'water employed within the limits specified, increases the efiective vapor pressures of the impurities relative to the vapor pressure of the alcohol being purified, thus allowing the impurities to pass overhead from the distillation zone. Although it is preferable not to have any plates in the tower above the water feed plate, it is possible to carry out the separation with a limited number of plates above the water feed plate. However, this number should be held to a minimum.

Although the invention has been described employing pure water in the distillation process, it is also permissible in the purification of alcohols to use water containing a small amount of salts, such as sodium acetate, or acid, such as sulfuric acid or even caustic, such as sodium hydroxide.

' Although the invention has been illustrated by the purification of isopropanol, it is equally applicable to the purification of other alcohols of 2 to 5 carbon atoms per molecule resulting from the reaction of mono-olefins, such as ethanol, tertiary butanol, secondary butanol, the secondary amyl alcohols, and tertiary amyl alcohol. In this regard the impurities are removed in a' manner similar to that described for the isopropanol system. The following are approximate typical compositions of some of the crude aqueous alcohols which may be treated according to this purification process:

CRUDE ETHYL Ancorron 80-85 weight per cent ethyl alcohol 9-14 weight per cent ethyl ether 0.2-0.8 weight per cent hydrocarbons (B. P.

2.5-5 weight per cent colloidal carbon CRUDE SECONDARY BUTYL ALCOHOL 75 weight per cent butyl alcohol 5 weight per cent secondary butyl ether 4 weight per cent polymer oils Balance water and other impurities CRUDE SECONDARY AMYL ALCOHOL-S 50 volume per cent sec-amyl alcohol 20 volume per cent hydrocarbons 5-10 volume per cent sec-butyl alcohol 2-5 volume per cent tertiary amyl alcohol 5-1-0 volume per cent water 2-3 volume per cent ethers, e. g. sec-amyl, secbutyl and mixed ethers 2-5 volume per cent higher alcohols, e. g. hexyl alcohols 1-.2 volume per cent ketones, e. g. diethyl ketone of methyl propyl ketone composition of lid-99.9 mol per cent waterginjthe? liquid phase in the columm. For-secondaryamyl alcoholssufiicientqwater.should be added torn-aimtainpacomposition of 9!7.5 to: 99.9 molrpert cent waterintheliquid phaseinthecclumm The. following data: obtained: within plate, extractive distillation ,columm. indicat'eia that .1 the use of a; selective refluxg'sdoes notgreatly: affect. the quality: of." the recovered 1 product... The data; reported in Table I'werei obtained in the purifleae tion; of a crude isopropanol solution obtained" by: then sulfuric acids-catalysed; hydration of: propyl' ene. 1. The crudealcohol was fed to rthe 40th plate of the column while the; solvent water. was added to the 55th plate The selective; reflux, was',ob-" tained :by; feeding the: organic: phase 1 or the 1 condens'ede overlieadl'toxa ithreeestaget countercurrent water :"ext'ractor. l The water 1 extract (phases was thenpumped back to the top of the columnito gether with. thew'ateri phase of the condensed distillate.

TAnnE r 55 Plate'labomtorytcolumn w of the: components.regardlessuof the direction in whicltth'ey are-separated: i ilhatais claimed? is l l 1 lam. the separation; of organic component" A 0479a... an

confident al- 1. PILOL'I! :ennN'r None 93. 5 96-98 11.6 21. 5 Selective reflux.-- 92. 5 96-98 12. 5 25. l

from organic c'omponenttB-byextractivexdistil lationi wherein components-A- and arewintro duced into a; fractional;distillationrzone "at? ant intermediate point: thereofo wherein. distilla-i' 'GiOl'lTSGIVGnt is introduced intoltheifractional dis-p:

B93. tillation' zone ata-point aboveathepointof intro duction" oil components and B1 and heat applied no effect vaporization of the: components one of which is removed overhead-dram. the extractive distillation zone as e. vapor and the: other as 1 51 bottoms dissolved ih the solvent; and wherein theoverhead{ condenses into a; "s'ol ven non-solvent phaseccntaimn" qu bottomscomponen the" i comprises e'xt'ra" the the difstillation 'solvent an I and the solven t phase tothe distillation zones Optical Density of;

Percent Product ooLnM-N In comparison with distilled water. these wave lengths.

Object of Distillation Extractive Distillation Solvent Separation of close-boiling a1c0- hols, e. g. ETOH (overhead) fromIPOH (bottoms) i-BuOH (overhead) from N-BuOH (bottoms), etc.

Separation of alcohols (bottoms) from non-alcoholic oxygenated compounds (overhead).

Dehydration of alcohols Separation of acetone from neutral oxy compounds.

Separation of MEK from SBOH.

Separation of aromatic hydrocarbon isomers or of different types of aromatic hydrocarbons.

Separation of paraflins from olefins, olefins from diolefins.

Higher alcohols, snlfolane, phenol, glycols, glycol ethers, esters, ether-esters, hydrocarbons, salts, etc.

H20 (fill-99.9 mol percent, preferably 85-99 mol percent).

Water immiscible alcohols, gasoline, etc. Water.

Do. Hydrotropic salts, e. g. 'sulfonates, etc.

Acetone, furiural, etc.

The process is applicable Whether the desired component is being recovered overhead from the extractive distillation tower or whether it is recovered as a solution in the solvent at the bottom of the tower, since the purpose of the solvent is to improve the relative volatility (alpha) Odor of alcohol increases with increasing optical density at I 2. The method of refining a crude aliphatic alcohol produced by reaction of a mono-olefin, said crude alcohol containing contaminants lower boiling and higher boiling than the alcohol, which comprises continuously feeding the crude alcohol to a fractional distillation zone at an intermediate point thereof, continuously feeding sufiicient water to the fractional distillation zone at a point substantially above the crude alcohol feed point to maintain an internal liquid reflux having a water content in the range of 65-99.9 mol per cent water below the point of addition of the water, distilling from said crude alcohol a vaporous mixture comprising both lower boiling and higher boiling contaminants and quantities up to 5 vol. of the aliphatic alcohol wherein the vaporous mixture flows countercurrent to the internal aqueous liquid reflux, removing the vaporous mixture overhead from the fractional distillation zone, condensing the overhead to form an aqueous phase and a non-aqueous phase, extracting the non-aqueous phase with water to form a second aqueous phase and a second nonaqueous phase, introducing both aqueous phases to the distillation zone and withdrawing a dilute aqueous solution of the alcohol freed of the thus distilled contaminants from a lower portion of said fractional distillation zone.

3. Th method of claim 2 in which the alcohol is a C2-C5 aliphatic alcohol.

4. The method of refining crude isopropanol produced by the reaction of propylene, said crude isopropanol containing contaminants lower boiling and higher boiling than the isopropanol, which comprises continuously feeding crude iso-. propanolto a fractional distillation zone at an intermediate point thereof, continuously feeding sufficient water to the fractionaldistillation zone at a point to maintain an internal liquid reflux having a water content in the range of 70-99 molper cent water below the point of addition of the water, distilling from said crude isopro-. panola vaporous mixture comprising both higher boiling and ,lower boiling contaminants and quantities up to vol. of isopropanol:wherein the vaporous mixture flows countercurrent to the internal aqueous liquid reflux, removing and condensin the vaporous mixture overhead from the fractionaL distillation zone, whereby an.

6. The method of refining crude sec-butanol produced by the reaction of n-butenes, said crude sec-butanol containing contaminants lower boiling and higher boiling than the sec-butanol, which comprises continuously feeding crude sec-butanol to a fractional distillation zone at an intermediate point thereof, continuously feeding sufiicient water to the fractional distillation zone at a point to maintain an internal liquid reflux having a water content in the range of -999 mol percent water below the poi'ntof addition of the water; distilling from said' crude sec-butanol a Vaporou's' mixture comprisingi both higher boiling and .lower lboilinggx'ontaminants and quantities union-m1: 'sof sec'butanol wherein .the vaporous mixture flows 'countercurrent to the internal aqueous: liquid'refiux; re-* moving and condensing theivaporousimixture overhead from the fractionalLdistillati'on zone,

whereby an aqueous .phaseand anon-aqueous phase are formed, extracting the non-aqueous phase with water to form a second aqueous phase and an organic rafflnate phase; refluxin -both aqueous phases to the distillation zone;fan'd withdrawing a dilute aqueous solution of sec-butanol freed of the thus distilled contaminants; from a lower portion of said fractional distillation zone. v n

WILLIAM M; DRoUrJR;

REFERENCES CITED The following references are of record in the file ofthis-patentzf UNITED STATES PATENTS Number Name Date 996,328 Guillaume June 27, 1911 1,929,901 Ricard et a1. Oct. 10, 1933 2,148,846 Von Retze et a1. Feb. 28, 1939 2,198,651 Bludworth Apr. 30, 1940' 2,290,442 Metzl July 21, 1942 2,324,755 Beamer July'20, 1943 2,339,160 Dunn et al. Jan.'11, 1944 2,360,655 Deanesly Oct. 17, 1944' 2,377,049 Souders May 29, 1945 

1. IN THE SEPARATION OF ORGANIC COMPONENT A FROM ORGANIC COMPONENT B BY EXTRACTIVE DISTILLATION WHEREIN COMPONENTS A AND B ARE INTRODUCED INTO A FRACTIONAL DISTILLATION ZONE AT AN INTERMEDIATE POINT THEREOF, WHEREIN A DISTILLATION SOLVENT IS INTRODUCED INTO THE FRACTIONAL DISTILLATION ZONE AT A POINT ABOVE THE POINT OF INTRODUCTION OF COMPONENTS A AND B AND HEAT APPLIED TO EFFECT VAPORIZATION OF THE COMPONENTS ONE OF WHICH IS REMOVED OVERHEAD FROM THE EXTRACTIVE DISTILLATION ZONE AS A VAPOR AND THE OTHER AS BOTTOMS DISSOLVED IN THE SOLVENT, AND WHEREIN THE OVERHEAD CONDENSES INTO A SOLVENT PHASE AND A NON-SOLVENT PHASE CONTAINING QUANTITIES OF THE BOTTOMS COMPONENT, THE IMPROVEMENT WHICH 